1. Technical Field
The present invention relates generally to fluid level sensing systems in which the level control is accomplished through the use of a displacement member whose motion is transmitted to a pneumatic or electric controller which is connected to a process valve, and specifically, to an improved pneumatic controller for such systems.
2. Description of the Related Art
The oil and gas, chemical and other industries utilize process valves for the control of process fluids which are operated by means of a pneumatic or electrical control signal. The controller for such valves typically includes a pilot valve whose function is to generate an output signal pressure which either opens or closes the process valve. In the typical prior art system, the level of liquid in the tank or other container is sensed with a displacement element or float that is in communication with the liquid in the container. The displacement element transmits a force or movement to the controller that is situated outside the container. The force or displacement so sensed is a measure of the change in liquid level.
For example, in the case of an oil and gas separator tank, a liquid level controller is provided which uses a float or displacement type sensor to transmit changes in the liquid level in the tank to a pilot valve outside the vessel. The pilot valve signals a process control or discharge valve in the discharge outlet from the vessel to open or close the discharge valve in response to the liquid level within the vessel.
Supply gas is generally taken from the production gas and routed to the pilot valve. When the liquid level in the vessel is within the desired limit, the supply gas is vented through the pilot valve to the atmosphere. When the liquid level rises sufficiently to change the position of the float, a flapper applies a force to the pilot valve so that the supply gas is diverted within the pilot valve to thereby provide a control signal to the discharge valve which allows liquid to flow from the vessel.
Many of the prior art liquid level controllers require right or left hand mounting which requires that both mountings be available in inventory. Also, their conversion between such mountings requires extensive reworking of the mounting and the components. It was often difficult to reach the internal components of such devices for repair and reconfiguration. Typically, the control systems were totally enclosed in a housing. The housing was required to be sealed to the atmosphere. Where a supply gas filter was present, it was generally difficult to access and clean as these steps required accessing the housing interior before access to the filter housing could be obtained. Also, the pressure gages were typically inside the housing and removal of the housing was required to service the gages. As a result, the components of the typical prior art pneumatic pilot level controller were not easily accessible or easily removed for maintenance or replacement
In many cases, an adjustable biasing spring was used to balance the force exerted by the weight of the displacement element or float. The adjustable biasing spring was also enclosed within the housing in some cases, thereby making any adjustment of the biasing spring difficult and time consuming.
A need exists for a liquid level controller which can be easily and quickly accessed for adjustment or repair.
A need also exists for such a controller which features an externally mounted pilot assembly and filter assembly.
A need also exists for such a controller which features externally mounted pressure gauges which are oriented to accommodate either left or right hand mountings.
A need also exists for such a system that can enable adjustment of the biasing spring without having to remove the housing cover.
A need also exists for such a liquid level controller which is simple in design and economical to manufacture, which is dependable in operation and which features fewer parts than the prior designs.
It is therefore one object of the present invention to provide an improved liquid level controller which utilizes an easily adjustable spring counterbalance.
Another object of the invention is to provide a liquid level controller having an externally mounted pneumatic pilot and also having an externally mounted supply gas filter housing with an improved filter arrangement which facilitates maintenance or replacement of the filter element.
Another object of the invention is to provide a liquid level controller having an improved pressure gauge arrangement that facilitates viewing of the pressure gauges.
Another object of the present invention is to provide an improved liquid level controller which is simple in design, economical to manufacture and is dependable in operation.
The foregoing objects are achieved with the improved liquid level controller of the invention. The level controller of the invention has a pneumatic pilot assembly located outside the main housing. Because the pneumatic pilot assembly is outside the main housing, the component parts are easy to replace and repair. The filter housing is also located outside the main housing. The location of the filter housing facilitates maintenance or replacement of the filter element. An adjustment screw for the spring counterbalance is accessible without removal of the housing cover.
In a preferred embodiment, the improved liquid level controller of the invention includes a main housing having a plurality of walls which together define a normally enclosed interior, the main housing having a tubular connector body located on an exterior surface of a selected sidewall of the main housing. The connector body is connectable to a sidewall of a liquid containing vessel for communicating with an interior of the vessel.
A torque bar is located within the main housing closed interior. The torque bar is pivotally mounted therein by means of a torque shaft attached at a pivot end of the torque bar and extending generally perpendicular thereto. The torque shaft is supported by inner and outer bearing assemblies, the inner bearing assembly being located within a selected sidewall of the main housing and the outer bearing assembly being located within a sidewall of the connector body.
A displacement shaft has a first end connected to the torque shaft and extending perpendicular thereto. The displacement shaft also has a second end which extends through a bore provided within the tubular connector body to a liquid displacement member for transmitting vertical forces responsive to changes in liquid level as a force tending to rotate the torque shaft.
A lever is pivotally mounted within the main housing interior. An adjustable connector member interconnects the torque bar and lever for transmitting force exerted on the torque shaft to the lever. A biasing element located within the main housing interior contacts the torque bar to thereby balance force exerted on the torque bar by the liquid displacement member acting on the torque shaft.
A pilot assembly is located in a pilot housing which is mounted on the main housing and exterior thereto. The pilot assembly is actuable by movement of the lever to provide a selectable output for controlling a variable and desired liquid level within the vessel interior.
The foregoing objects of the invention, as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.